1. Field of the Invention
The present invention relates to a display device having a display tube including a cold cathode, more specifically a PN emitter.
2. Description of the Related Art
Display tubes having PN emitters are known in the art. A PN emitter, which is one example of a "cold cathode", is essentially a particular kind of semiconductor diode driven in avalanche breakdown, where the escaped "hot" electrons generate the emission current. Using such a device reduces the drive voltage to typically between 5 and 10 volts, while "hot cathodes" need 120 to 150 volts. This advantage of PN emitters makes it possible to consider developing a low voltage driver (IC) for the PN emitter. However, if display tubes having PN emitters are driven in the same way as display tubes having "hot cathodes", several problems occur. The voltage-current characteristic or drive characteristic of PN emitters is extremely steep and rather different compared to present day tube characteristics. A present day drive circuit would therefore be impractical due to the extremely high gain in the voltage-current characteristic. A further problem is formed by the diode efficiency of a PN emitter, i.e., the emission current of the PN emitter divided by the current passing through the diode. Typical values of the diode efficiency range between 1% and 5%. The efficiency varies not only as a function of time but also from device to device. This must be allowed for in some way.